The invention relates to a method of determining the level of the interface of two or more immiscible or partly-miscible fluids within a closed vessel. The level of any emulsion formed by the fluids may also be determined. In general, three or more stationary energy sources are positioned adjacent to the vessel, and stationary energy sensors are positioned to detect the level of intensity of energy exiting the vessel. Each energy source is sequentially activated and a set of intensities for each energy source is detected by the array of sensors and recorded. The aggregate of the sets of intensities is analyzed using an algorithm to determine the fluid levels. The method is based on the principle that materials of different densities often possess different energy adsorption coefficients. With the path length of the system being held constant, the degree of adsorption is correlatable with the density of the medium penetrated. Systems to detect the levels of fluid within a closed vessel are known in the art, but the method described herein provides an increased level of accuracy with greater ease of operation and maintenance.
Several systems described in the art require that the energy source be movable; see U.S. Pat. Nos. 3,668,392, 2,714,167, and 5,509,460. In some cases, a single sensor is moved in tandem with the movement of the energy source. Although successful, equipping the systems with the apparatus necessary for the precise movements of the energy source and maintaining that apparatus may be costly.
Other systems have provided multiple stationary energy sources each with its own individual corresponding sensor or array of sensors; see U.S. Pat. Nos. 4,228,353, 4,471,223, 4,038,548 and 3,170,064. U.S. Pat. No. 4,471,223 also discloses a single radiation source and an array of sensors. Another approach has been to insert the energy source and a detector, or source-sensor pairs, invasively into the vessel such as described in U.S. Pat. Nos. 3,654,458 and 4,904,878. Still another approach has been to use an energy source an sensor attached to a vertical standpipe in fluid communication with the vessel containing the fluids whose interface level is to be determined such as described in EP 330 123-A2. The standpipe is positioned so that the interface levels in the standpipe correspond to the same levels as those in the vessel.
The present invention provides a method of determining the level of fluid interface within a closed vessel that is noninvasive, has low maintenance, is accurate and cost effective. Furthermore, the necessary apparatus is easy to install on existing vessels thereby making retrofit applications economically attractive. The method of the present invention provides greater detail and accuracy than those previously available by analyzing an aggregate of recorded sets of data where each data set contains intensity measurements corresponding to different energy sources.